High-throughput lithography and surface patterning with extremely fine linewidths (e.g., on the order of 10-100 nm) are very important for the future growth of the microelectronics industry and nanotechnology. Next-generation integrated circuit technology will inevitably call for efficient and low-cost generation of features with a sub-100-nm linewidth. The emerging field of nanotechnology also requires patterning and functionalization of surfaces with a spatial resolution that is comparable with the scale of the molecules and cells that need to be manipulated and modified.
The resolution of conventional projection optical lithographic systems, still the most widely used in the microelectronics industry, is limited by optical diffraction. The resolution can be improved by using beam-based direct-writing tools with high energy and short wavelengths. High-energy beam lines, including ones that rely on electron beams and X-rays, are being used. However, such direct-write lithography systems suffer from several drawbacks. First, such systems are invariably complex and expensive. Second, these lithographic tools operate with a single beam and produce patterns in a serial manner, resulting in low throughput. Third, conventional high resolution lithography systems are not capable of depositing patterns made of biological molecules or chemical compounds. Only special chemical resists may be used.
Dip-pen Nanolithography (DPN) is a new and recently introduced method of scanning probe nanolithography. A description of DPN is contained in PCT/US00/00319, the entirety of which is incorporated herein by reference. It functions by depositing nanoscale patterns on surfaces using the diffusion of a chemical species from a scanning probe tip to the surface, sometimes via a water meniscus that naturally forms between tip and sample under ambient conditions. As a DPN tip is scanned across the surface of a substrate, molecules on the surface of the tip are transported through the water meniscus that forms between the tip and the substrate surface. Once on the surface, the molecules chemically anchor themselves to the substrate, forming robust patterns. Features in the 10 nm to many micrometer range can be fabricated with commercially available silicon nitride tips. One factor that influences the linewidth of DPN writing is the linear speed of the tip. Smaller linewidths are achieved with faster tip speeds. Other factors that influence the linewidth include the sharpness of the DPN tip and the diffusion constants of the molecules used as inks.
DPN offers a number of unique benefits, including direct writing capability, high resolution (˜10 nm linewidth resolution, ultimate ˜5 nm spatial resolution), ultrahigh nanostructure registration capabilities, the flexibility to employ a variety of molecules for writing compounds (including biomolecules) and writing substrates (such as Au, SiO2, and GaAs), the ability to integrate multiple chemical or biochemical functionalities on a single “nano-chip”, a one-layer process for patterning, and the ability to automate patterning using customized software.
DPN technology can be implemented using a low-cost commercial scanning probe microscope (SPM) instrument. In a typical setup, the DPN probe chip is mounted on an SPM scanner tube in a manner similar to commercially available SPM tips. Precise horizontal and vertical movement of the probes is attained by using the internal laser signal feedback control system of the SPM machine.